Pulp forming die



April 8, 1958 C J. CHAPLIN PULP FORMING DIE 2 Sheets-Sheet 1 Filed April 5, 195"! April 1958 c. J. CHAPLIN 2,829,568

PULP FORMING DIE Filed April 5, 1957 2 Sheets-Sheet 2 United States Patent PULP FORMING DIE Application April 5, 1957, Serial No. 650,939

3 Claims. (Cl. 92--57) This invention relates to apparatus useful for molding fibrous pulp articles and more particularly to a novel forming die structure for suchapparatus.

In the manufacture of articles by pulp molding processes, a foraminous die, having on one side thereof a molding surface contoured to form an article of the desired shape, is immersed with its molding surface downward in an aqueous dispersion of fibrous material such as wood pulp and suction is applied to its opposite side to accrete said fibrous material on said molding surface. Conventionally, such a die is provided with a multiplicity of drilled holes communicating from its molding surface to its opposite surface, the molding or forming surface usually being provided with a fine wire screen covering and the opposite or suction surface of the die being mounted on suitable apparatus so that it forms one wall of a suction chamber to which suction is applied during the forming operation to accrete the fibrous material on the screen by moving its suspending liquid through the die into the suction chamber. Although the forming dies heretofore used in the art have been widely used, they not only had a tendency to clog because of the-plugging of themultiplicity of small drilled holes therein and as a result to produce non-uniform articles, but they were also unduly heavy and expensive to manufacture. Thus, if the drilled holes were made small enough so that the fine wire screen was adequately supported, the multiplicity of holes were both difficult and costly to provide, and if the holes were made large enough so that they were less expensive to drill and did not plug or clog, they did not form an adequate support for the fine wire screen and caused marking.

Accordingly, it is an object of the present invention to provide a novel, light-weight yet strong forming die which is particularly economical to manufacture and which has reduced clogging tendencies yet provides adequate support for the die covering. This has been accomplished by providing a die body having a rib structure on the suction chamber side thereof and by cutting a plurality of slots through the wall of said die body in a direction across the ribs yet without severingthem so thatthe integrity of the die structure is maintained by .holding it together in a direction across the slots. This not only makes possible the provision of a foraminous.

die body by the cutting of slots rather than by the drilling of a plurality of holes, but also makes possible the use of extraordinarily thin walls to provide a light weight die body without reducing die strength. Furthermore, not only. do the slots have less tendency to clog than do suitably small holes, and yet, since they extend across the ribs along the forming surface, provide uniform accretion, but the spacing between the slots can be made even less than the spacing between drilled holes, thereby providing adequate die drainage, and yet the very narrowness of the slots prevents the wire screen covering from becoming distorted by being pressed into the slots.

For the purpose of more fully explaining preferred embodiments of my invention, reference is now made to the following detailed description, taken together with the accompanying drawings, wherein:

Fig. 1 is a plan view partially broken away of a formingdie of the invention taken from the forming side thereof;

Fig. 2 is a cross-sectional elevation of the die of Fig. 1 taken on the line 2-2 thereof;

Fig. 3 is a cross-sectional view of the die of Figs. 1 and 2 taken on the line 3-3 of Fig. 2;

Fig. 4 is a plan view of the bottom closure member of the die of Figs. 1 and 2; i

Fig. 5 is a cross-sectional elevation of the botto closure member of Fig. 4 taken on the line 5--5 thereof;

Fig. 6 is an overall plan view of a modification of the forming die of the invention taken from the forming side thereof;

Fig. 7 is an enlarged plan view of a portion of the forming die of Fig. 6 taken from the forming side thereof;

Pig. 8 is an enlarged plan view of a portion of the forming die of Fig. 6 taken from the suction chamber side thereof;

Fig. 9 is an enlarged cross-sectional view taken on the line 99 of Fig. 7; and i Fig. 10 is an enlarged isometric view of a modificatio of the forming die of Fig. 6.

Referring to Figs. 1 through 5, the forming die shown includes a hollow generally frusto-conical body portion generally designated 10 having a forming screen 12 on its contoured molding surface and a bottom closure member therefor generally designated 14 and having a forming screen 16. The bottom closure member 14 also functions as a clamp ring for retaining forming screens 12 and 16 on their molding surfaces at one end of said body portion. A clamp ring 18 is provided at the other end of body portion 10 both for clamping the other end of the body portion formingscreen 12 and for mounting the forming die on the suction chamber walls 20 of a conventional pulp molding machine (not shown) to form one wall thereof.

According to the present invention, the body portion 10 has a relatively thin wall 22 and is provided generally centrally on the suction chamber side thereof with an integral circular reinforcing rib 24 extending therearound and projecting for a substantial distance above the surface of wall 22 on the suction chamber side of body portion 10. Preferably, a similar rib 26 is provided at the end of body portion 10 adjacent end closure member 14 both for reasons of strength and to act as a flange for the' mounting of said end closure member on the body portion. Likewise, a rib 28 is provided at the other end of body portion 10 and acts, together with clamp. ring 18, as a flange for the mounting of the assembled forming die structure on the suction chamber walls 20 of a pulp molding machine. In order to provide the necessary apertures through the forming die body portion 10, a plurality of generally parallel narrow slots 30 areuni formly distributed over the entire molding surface of said body portion, said slots 30 extending across the ribs 24, 26 and 28 in a direction generally perpendicular thereto and axially of said body portion. Each ofthe slots 30 communicates through the wall 22 from the molding surface side thereof to the suction chamber side thereof at each side of central rib 24 and between said central rib and each of ribs 26 and 28, and are of substantial, generally uniform depth across each of the ribs 24, 26 and 28 throughout their entire length. However, to maintain the integrity of each of said nbs as a peripheral support for the body portion 10, the slots 30 must terminate short of at least a portion of the projecting portion of each of said ribs and preferably said slots extend no deeper than just beyond the suction chamber surface of Patented Apr. 8, 8

wall 22 to ensure that said slots communicate through i said wall. Thus, slots are provided throughout the entire extent of the molding surface of body portion 10 and its forming wire 12 thereafter applied bridges said slots to provide a screen surface covering said slots over the entire molding surface of said body portion. The abutting edges of the wire 12 are clamped together in a slot 34 extending generally axially of the body portion 10 along one side thereof, this latter'feature being in accord with the teachings of Patents 2,326,758 and 2,359,201.

Referring for the moment to Fig. 8, wherein is indicated by dotted circles the approximate size of drilled holes which would be necessary in order to provide drainage equal to that provided by the slots 54, it is apparent that said holes have a much greater distance across which the wire 48 must bridge than do the slots, in fact, of the order of three or four times greater. Fequently, the wire becomes depressed in these necessarily large holes or openings and hence causes an unsightly surface on the molded product by marking said surface with circular protuberances corresponding-in diameter to said holes.

1 To provide proper drainage at end closure member 14, a plurality of slots 36 are provided communicating therethrough, but terminating short of the center thereof to maintain the integrity of said member, said bottom member being sufiiciently strong without the need for a strengthening rib. If desired, a central post 38 may be mounted on said closure member 14.

In the operation of theabove described structure, when suction is applied thereto and the molding surface thereof is immersed in a liquid-fiber mixture in the usual manner, the fiber will be accreted on the surface of forming wire 12 and 14 and provide an article, such as a flowerpot, of the shape of said surface and having a central hole'in its end closure corresponding to the diameter of post 38 adjacent the wire 16.

Referring now to Figs. 6 through 9 wherein is shown a modified forming die structure for molding an article such as a molded fiber plate, it will be noted that the entire die structure may be made integal with a. hollow, generally frusto-conical body portion 42 having at its one end an integral outer flange or rim portion 44 for mounting said die as a wall of the suction chamber of a: suitable, pulp molding machine and merging at its other end with an end closure portion 46, the molding surface of said die being covered by wire 48.

In accordance with the present invention, said body portion and its merging end closure portion 46 has a relatively thin wall 50 and is provided generally at the point of merger of said body portion with said end closure potion with an integral circular reinforcing rib 52 extending therearound and projecting for a substantial distance above wall 50 on the suction chamber side of the forming die, and a plurality of uniformly distributed generally parallel slots 54 extending from flange portion 44 nearly to the center of end closure portion 46. Said slots communicate through the wall 50 and extend across rib 52 yet terminate short of at least a portion of its projecting portion to maintain the integrity thereof, so that substantially the entire extent of the molding surface is provided with slots with the forming wire 48 bridging said slots to provide a screen surface covering said slots over the entire molding surface of the body portion, the peripheral edge of said wire 48 being suitably clamped at flange 44 by any suitable means (not shown). Preferably, radial ribs 56 may be provided on the suction chamber side of the die to permit the use of a thinner wall 50. If desired, as shown in Fig. 10, shallow circular grooves 58 may be provided on the molding surface side of the die both to aid drainage between the slots and to produce an attractive finish on the interior surface of the formed article,

Thus it will be seen that the invention provides a novel light-weight yet strong forming die having substantial advantages in manufacture and performance over heretofore known forming dies. Various modifications of my novel forming die structure within the spirit of my invention and the scope of the appended claims will be apparent to those skilled in the art.

I claim:

1. A forming die for molding fibrous pulp articles including a thin walled body portion having a suction chamber side and an article forming side with a contoured molding surface and a forming screen on said contoured molding surface in contact therewith, said body portion having on the suction chamber side thereof in- F tegral rib means projecting above the surface thereof and a plurality of narrow slots extending in a direction across said rib means and communicating through the wall of said body portion from the molding surface side thereof to the suction chamber side thereof and terminating short of at least a portion of said rib means projecting above the suction chamber side surface to maintain the integrity of said rib means as a peripheral support for said slotted body portion and to provide slots in said molding surface across a substantial portion of said rib means, said forming screen bridging said slots to provide a screen surface covering said slots. I

2. A forming die for molding fibrous pulp articles including a thin walled body portion having a suction chamber side and an article forming side with a contoured molding surface and a forming screen on said contoured molding surface in contact therewith, said body portion having on the suction chamber side thereof integral rib means extending therearound and projecting above the surface thereof and a plurality of generally parallel narrow slots extending across said rib means in a direction generally perpendicular thereto and communicating through the wall of said body portion from the molding surface side thereof to the suction chamber side thereof on each side of said rib and at said rib and terminating short of at least a portion of said rib means projecting above the suction chamber side surface to maintain the integrity of said rib means as a peripheral support for said slotted body portionand to provide slots in said molding surface across said rib means, said forming screen bridging said slots to provide a screen surface covering said slots over substantially the entire molding surface of said body portion. a

3. A forming die for molding fibrous pulp articles including a hollow thin walled body portion of generally frusto-conical shape having a suction chamber side and an article forming side with a contoured molding surface and a forming screen on said contoured molding surface in contact therewith, said body portion having on the suction chamber side thereof a circular integral rib extending therearound and projecting above the surface thereof and a plurality of generally parallel narrow slots distributed over the entire molding surface of said body portion extendingacross said rib means in a direction generally perpendicular thereto and axially of said body portion communicating through the wall of said body portion from the molding surface side thereof to the suction chamber side thereof on each side of said rib and at said rib and terminating short of at least a portion of said rib means projecting above the suction chamber side surface to maintain the integrity of said rib as a peripheral support for said slotted body portion and to provide slots in said molding surface across. said ribs, said forming screen bridging said slots to provide a screen surface covering said slots over substantially the entire molding surface of said body portion.

No references cited. 

